1. Field of the Invention
The present invention relates to hopped malt beverages, especially alcoholic brewery beverages produced at least in part from malt. More particularly, the present invention relates to imparting to hopped malt beverages improved stability against light-induced off flavors.
2. Description of Related Art
As is well known and accepted in the malt beverage brewing art, subjecting a hopped malt brewery beverage, especially an alcoholic hopped malt brewery beverage, such as, lager, ale, porter, stout, and the like (herein generically referred to as “beer”) to sunlight or artificial light results in a significantly deleterious effect on the sensory qualities of the beverage by generating a so-called “skunky” flavor, which is sometimes also referred to as “sunstruck” or “light struck” flavor. It is believed that the skunky flavor is due to photochemical changes in the beverage that produce volatile sulfur-containing compounds. These sulfur compounds are thought to be formed at least in part by reaction of other sulfur-containing compounds with photochemically degraded hop components in the beverage. Only very small amounts of these sulfur compounds are required to be present to impart the skunky flavor to the beverage and render it unacceptable. The photochemical reaction is assisted by the presence of riboflavin, one of several photo-initiators in the beverage, the riboflavin emanating mainly from the malt used in the production of beer and to a minor extent via the hops and, according to the common wisdom, the action of yeast during the fermentation (See Tamer et al. Enzyme Microb Technology 10:754–756 (December, 1988)).
Attempts to prevent beverages from becoming skunky involve enclosing the beer bottles made of protective, i.e., colored, glass, brown or amber being most efficient (see U.S. Pat. No. 2,452,968), or in cans. These bottles reduce or eliminate the transmission to the beverage of light of wavelength shorter than about 560 nanometers. Such light is most harmful because it assists the riboflavin in enhancing the production of the undesirable volatile sulfur compounds.
Another method developed to address the problem of “skunky” flavor production uses reduced isohumulones in place of hops or hop extracts (see Verzele, M., et al., U. Inst. Brew. 73:255–257, (1967)). Other methods involve adding light-stabilizing materials to the beverage (see U.S. Pat. No. 4,389,421). However, in some jurisdictions, the use of such compounds has not been approved and, further, many brewers are reluctant to use any additives at all, but, rather, still use hops or hop extracts in an effort to achieve traditional beer flavor.
The problem of skunky flavor has been the subject of research for many years, and such research continues (see Sakuma, et al., “Sunstruck Flavor Formation in Beer,” American Society of Brewing Chemists, Inc. (1991), 162–165). This article also deals with the part believed to be played by riboflavin in the reaction that produces the skunky flavor and suggests that removing riboflavin from the finished beer may solve the problem. However, an acceptable means for achieving that suggestion has not been readily apparent, and the problem persists.
The most favorable context in which light is used in association with malt beverages is described in U.S. Pat. No. 3,787,587. There, an actinic light treatment on finished beer is used to accelerate the “aging” and “maturing” thereof. Moreover, sunlight or artificial light was used as early as 1865 (see U.S. Pat. No. 50,523) to treat the surface of boiling wort to decolorize it. The boiling wort, in keeping with typical brewery practices, would presumably have been hopped and open to a highly oxygenated atmosphere during the boiling treatment. In both of these processes, it is highly probable that skunky beer flavor would ensue in the finished product. This is in keeping with what is well known in the art about photochemical degradation in hopped malt beverages. It is also in keeping with the general view that exposure of beer to light is anathema and should be avoided at all costs in the interest of maintaining product shelf life.
The literature also teaches a process in which sake, a unique Japanese fermented liquor prepared using rice, has been subjected to a light treatment (see Japanese published Patent Application 67667, entitled “Process for Production of Sake Hardly Affected by Microbial Deterioration”). This publication discloses treating finished sake with light in the 200- to 700-micron range—the object being to have the light decompose the riboflavin present in the finished sake, which riboflavin is an essential nutrient for the lactic acid bacteria that are responsible for infectious spoilage in finished sake. As a consequence of the riboflavin destruction, the growth of the bacteria is said to be inhibited and the sake preserved. Sake is, of course, a different product from beer, being an unhopped, non-malt product produced from rice using a starch-digestive enzyme, amylase, obtained from a mold and a special sake yeast to effect the fermentation. In particular, it should be noted that the riboflavin in sake, absent any lactic acid bacterial infection, does not pose the off-flavor development problems that are typically associated with hopped malt-containing products, such as, beer.
The role of light in the production of hopped malt beverages, and especially in brewing, has received a great deal of attention, and it is generally accepted that, in malt brewery beverages, especially those of an alcoholic nature, photochemical reactions produce accelerated aging and, in general, will shorten a malt beverage's shelf life and engender undesirable flavor development.